The photosensitive charge transfer devices to which the present invention relates are also known as "charged coupled devices" or "CCD" and they are generally of the area type although they may in special circumstances be linear. In either case, light radiation is applied to charge transfer registers. Such devices are now wellknown in themselves and are described, in particular, in the work by C. H. Sequin and M. F. Thompsett entitled "Charge transfer devices", page 142 et seq. The present invention is applicable to charge transfer devices which are linear charge coupled devices or surface area charge coupled devices using three or four control phases.
In prior art photosensitive charge transfer devices, the bias voltage applied to the charge transfer registers in the image zones and in the memory zones is fixed once and for all regardless of the level of illumination received by the image zone. However, this bias voltage determines the depth of the potential well created under said registers, in other words it determines the storage capacity of minority carriers. As a result, if the level of illumination is very much less than the chosen saturation level of illumination, the degree to which the potential wells are filled will be very small. Unfortunately, the depth of the potential wells has both direct and indirect effects on various features such as dark current, noise due to the control phases, etc.
The object of the present invention is to mitigate the above-mentioned drawbacks by providing a method of adjusting the operating conditions of a charge transfer device together with an apparatus for performing the method. In particular, the dark current, and consequently the power consumption can be reduced by implementing the invention, as can the noise due to the control phases.